Development of New Ultrasonic Measurement System for Turbulence and Elucidation of the Limit of Transport in Turbulence

湍流的研究在科学技术的各个领域都具有重要意义。其中热湍流是一个热门的研究课题，因为热湍流中的热输运、扩散和混合的预测是基础研究和应用研究不可缺少的内容。本研究旨在发展一种新的热湍流超声波测量方法，探索湍流中的狭窄结构，以阐明湍流引起的拍频输运的标度律。我们用水银作为测试液体。因为，它的运动粘度低，运动边界层比热边界层薄，这一事实使我们能够在实验室中探索高瑞利，高雷诺数。由于时间分辨率和可达到的最大速度的限制，它从未被应用于湍流测量。湍流，因为 ...更多信息 热湍流的最大速度和最高频率即使在高Rayleigh数下也相对较低，与其它湍流如网格湍流和尾流湍流相比。我们研制了三套热湍流测量系统.三个超声波传感器同时沿沿着X、Y和Z轴进行监测。2.一个移动的传感器，而不破坏对流单元的壁。3.多个温度传感器（32个热敏电阻）嵌入在单元底部和侧壁，使我们能够监测热湍流中的平均流的结构。利用这些测量系统，我们成功地测量了能量谱直接从瞬时测量的速度场没有使用泰勒假设，并发现Bolgiano-Obkhov标度律成立的热湍流。进一步阐明了存在于热湍流中的平均流的结构。它们的结构、动力学和稳定性强烈地依赖于对流单体的长宽比。少

Study on turbulence is important for every area of science and technology. Among them thermal turbulence has been popular research subjects, since the prediction of heat transport, diffusion and mixing in thermal turbulence is indispensable fur both fundamental and application researches. In this research project we aimed to develop a new ultrasonic measurement method far thermal turbulence and explore stricture in turbulence to elucidate the scaling law of beat transport due to turbulence. We used mercury as a test liquid. Because, the fact that its kinematic viscosity is low and kinetic boundary layer is thinner than the thermal boundary layer enables us to explore high Rayleigh, high Reynolds number in laboratory Although ultrasonic velocimeter (USV) is known for long time for flow rate measurements, it has never been applied to measurement of turbulence due to limitation in temporal resolution and accessible maximum velocity We succeeded to use USV for thermal turbulence, because t … More he maximum velocity and the highest frequency in thermal turbulence is relatively low even at high Rayleigh number compared with other turbulence, such as grid turbulence and wake turbulence. We developed 3 measurement systems far thermal turbulence 1. Three ultrasonic transducers monitoring along X, Y, and Z axes simultaneously. 2. One moving transducer without destructing the wall of the convection cell. 3. Multi-thermosensors (32 thermistors) embedded in the cell bottom and the side wall which enable us to monitor the structure of the mean flow in thermal turbulence. By using these measurement systems, we successfully measured the energy spectrum directly from instantaneous measurement of the velocity filed without utilizing Taylor hypothesis, and found that Bolgiano-Obkhov scaling law holds in thermal turbulence. We further elucidated structure of the mean flow existing in thermal turbulence. Their structures, dynamics, and stabilities strongly depend on the aspect ratio of the convection cell. Less